In random access information storage systems, a read/write head must be moved periodically and reliably in track seek operations between spaced apart data tracks on the storage disk to access desired information sectors randomly located on the disk tracks. Various servo control systems are known for controlling the acceleration and deceleration of the head during the track seek operation. Ideally, movement of the head is controlled in such a manner that it arrives over the target track at the end of track seek with zero velocity. At this time, control over movement of the head is handed off from the track seek servo control circuit to the track follower servo control circuit to maintain the track sensor located in the head centered on the desired track during read or write operation.
Various forms of tracking actuators are known to provide reasonably fast access time and good tracking control in magnetic disk drives of the aforementioned type. In a typical arrangement, the carriage for the read/write heads is mounted with ball bearing rollers on a pair of tracks, or races, and the carriage is driven by a stepper motor or voice coil motor to translate the head linearly in a radial direction over the data tracks formed on the surface of the recording disk. This arrangement has the advantage of providing a true linear tracking axis but has the disadvantage of imposing roller bearing irregularities that are not compatible with the extremely small, precise motions that are encountered in optical and magneto-optical drives.
There has recently been developed a tracking actuator system in which the read/write head is mounted between parallel elongated leaf springs, or flexures, to provide friction-free suspension that avoids the problems of track mounted actuators. A flexure-mounted head also offers the advantage of providing single stage tracking actuator operation in which the actuator motor servo controls provide both track seek and track following mode of operation thus simplifying the design of the objective lens actuator by limiting it to a single axis for focus control only. Such a single stage tracking actuator system is disclosed and claimed in copending application Ser. No. 287,801 assigned to the assignee of the present application.
Although advantageous for use in a single stage tracking actuator, particularly in optical and magneto-optical drives, a flexure mounted head presents certain problems with respect to the servo control employed in track seek and track following control modes of operation. Preferably, the head is mounted on the flexure ends such that when the flexures are in their at-rest (unflexed) condition, the head is positioned radially in the center of the band of data to be scanned by the head. Then as the head is scanned away from this at-rest position, the force required to move the head and hold it in position over the data track of interest increases as a function of the degree to which the flexures are bent away from their at rest position.
It is therefore an object of the present invention to provide a positioning system and method for a flexure mounted head actuator in a random access information storage disk drive system that compensates for the increasing restoring force of the flexures as the head is scanned away from its central, at-rest position.